U.S. patent application number 15/558743 was filed with the patent office on 2018-03-22 for method of removing a growth substrate from a layer sequence.
The applicant listed for this patent is OSRAM Opto Semiconductors GmbH. Invention is credited to Marco Englhard, Christoph Klemp.
Application Number | 20180082899 15/558743 |
Document ID | / |
Family ID | 55586282 |
Filed Date | 2018-03-22 |
United States Patent
Application |
20180082899 |
Kind Code |
A1 |
Klemp; Christoph ; et
al. |
March 22, 2018 |
METHOD OF REMOVING A GROWTH SUBSTRATE FROM A LAYER SEQUENCE
Abstract
A method of detaching a growth substrate from a layer sequence
includes introducing at least one wafer composite into an etching
bath containing an etching solution such that the etching solution
is located at least in regions within separating trenches,
repeatedly varying a pressure of a base pressure prevailing in the
etching bath with at least one pressure variation device, and
detaching the growth substrate, wherein at least one of 1-3 is
satisfied: 1) a buffer chamber attached to the etching bath and
connected thereto is provided and the volume variation is effected
by a movement of a piston or hydraulic plunger introduced into the
buffer chamber, 2) the volume variation is at least partly effected
with a compressor attached to the etching bath, and 3) the pressure
variation is at least partly effected by at least one of removal of
a gas and a liquid from the etching bath or by addition of at least
one of the gas and the liquid thereto.
Inventors: |
Klemp; Christoph;
(Regensburg, DE) ; Englhard; Marco; (Regensburg,
DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OSRAM Opto Semiconductors GmbH |
Regensburg |
|
DE |
|
|
Family ID: |
55586282 |
Appl. No.: |
15/558743 |
Filed: |
March 14, 2016 |
PCT Filed: |
March 14, 2016 |
PCT NO: |
PCT/EP2016/055454 |
371 Date: |
September 15, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/67092 20130101;
H01L 21/67086 20130101; H01L 21/30625 20130101; H01L 21/6835
20130101; H01L 33/0093 20200501; H01L 21/7806 20130101; H01L
2221/68381 20130101; H01L 31/1892 20130101; H01L 21/7813
20130101 |
International
Class: |
H01L 21/78 20060101
H01L021/78; H01L 21/306 20060101 H01L021/306; H01L 21/67 20060101
H01L021/67; H01L 21/683 20060101 H01L021/683; H01L 31/18 20060101
H01L031/18; H01L 33/00 20060101 H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2015 |
DE |
10 2015 104 147.2 |
Claims
1-13. (canceled)
14. A method of detaching a growth substrate from a layer sequence
comprising: A) providing at least one wafer composite comprising
the growth substrate, the layer sequence applied to the growth
substrate, and a carrier attached to a top surface of the layer
sequence remote from the growth substrate, wherein the layer
sequence is patterned in a multiplicity of regions spaced apart in
lateral directions and separated from one another by a multiplicity
of separating trenches, and the separating trenches connect to one
another, B) introducing the at least one wafer composite into an
etching bath containing an etching solution such that the etching
solution is located at least in regions within the separating
trenches, C) repeatedly varying a pressure of a base pressure
prevailing in the etching bath with at least one pressure variation
device, and D) detaching the growth substrate, wherein at least one
of A)-C) is satisfied: 1) prior to B) a buffer chamber attached to
the etching bath and connected thereto is provided and the volume
variation is effected by a movement of a piston or hydraulic
plunger introduced into the buffer chamber, 2) the volume variation
is at least partly effected with a compressor attached to the
etching bath, and 3) the pressure variation is at least partly
effected by at least one of removal of a gas and a liquid from the
etching bath or by addition of at least one of the gas and the
liquid thereto, the removal is effected with a first vacuum pump
connected to the etching bath and the addition is effected with a
gas inlet connected to the etching bath.
15. The method according to claim 14, wherein at least the etching
solution located within the separating trenches has gas bubbles,
the pressure variation giving rise to an alteration in the volume
of the gas bubbles and, accordingly, in a convection of the etching
solution within the separating trenches.
16. The method according to claim 14, wherein the pressure
variation comprises a temporal change between a maximum pressure,
corresponding to at least 2 times the base pressure, and a minimum
pressure corresponding to at most 0.2 times the base pressure.
17. The method according to claim 14, wherein the pressure
variation takes place temporally periodically at a variation
frequency of at least 0.01 Hz and at most 15 kHz.
18. The method according to claim 14, wherein the pressure
variation includes a volume variation between a minimum volume and
a maximum volume around a base volume of the etching bath, the
maximum volume corresponding to at least 3 times and the minimum
volume corresponding to at most 0.5 times the base volume.
19. The method according to claim 27, wherein prior to B) a buffer
chamber attached to the etching bath and connected thereto is
provided and the volume variation is effected by a movement of a
piston or hydraulic plunger introduced into the buffer chamber.
20. The method according to claim 27, wherein prior to B) a buffer
chamber attached to the etching bath and connected thereto and
having at least one variation valve is provided and the volume
variation is effected by closing and opening the variation
valve.
21. The method according to claim 27, wherein the volume variation
is at least partly effected with a compressor attached to the
etching bath.
22. The method according to claim 27, wherein the pressure
variation is at least partly effected by at least one of removal of
a gas and a liquid from the etching bath or by addition of at least
one of the gas and the liquid thereto.
23. The method according to claim 22, wherein the removal is
effected with a first vacuum pump connected to the etching bath and
the addition is effected with a gas inlet connected to the etching
bath.
24. The method according to claim 14, wherein prior to or during
C), the etching bath is introduced into an ultrasonic bath, and an
ultrasonic radiation is applied to the etching bath.
25. The method according to claim 14, wherein the etching bath is
heated using a heater to a process temperature which is at least
80.degree. C. and at most the temperature at the thermodynamic
critical point of the etching solution.
26. The method according to claim 14, wherein during steps B) to D)
a wedge is inserted between the growth substrate and the
carrier.
27. A method of detaching a growth substrate from a layer sequence
comprising: A) providing at least one wafer composite comprising
the growth substrate, the layer sequence applied to the growth
substrate, and a carrier attached to a top surface of the layer
sequence remote from the growth substrate, wherein the layer
sequence is patterned in a multiplicity of regions spaced apart in
lateral directions and separated from one another by a multiplicity
of separating trenches, and the separating trenches connect to one
another, B) introducing the at least one wafer composite into an
etching bath containing an etching solution such that the etching
solution is located at least in regions within the separating
trenches, C) repeatedly varying the pressure of a base pressure
prevailing in the etching bath using at least one pressure
variation device, and D) detaching the growth substrate.
Description
TECHNICAL FIELD
[0001] This disclosure relates to a method of removing a growth
substrate from a layer sequence.
BACKGROUND
[0002] DE 19734635 A1 describes a method of detaching a growth
substrate. There is a need to provide a simplified method of
detaching a growth substrate, especially non-destructively, from a
layer sequence.
SUMMARY
[0003] We provide a method of detaching a growth substrate from a
layer sequence including A) providing at least one wafer composite
including the growth substrate, the layer sequence applied to the
growth substrate, and a carrier attached to a top surface of the
layer sequence remote from the growth substrate, wherein the layer
sequence is patterned in a multiplicity of regions spaced apart in
lateral directions and separated from one another by a multiplicity
of separating trenches, and the separating trenches connect to one
another, B) introducing the at least one wafer composite into an
etching bath containing an etching solution such that the etching
solution is located at least in regions within the separating
trenches, C) repeatedly varying a pressure of a base pressure
prevailing in the etching bath with at least one pressure variation
device, and D) detaching the growth substrate, wherein at least one
of A)-C) is satisfied: 1) prior to B) a buffer chamber attached to
the etching bath and connected thereto is provided and the volume
variation is effected by a movement of a piston or hydraulic
plunger introduced into the buffer chamber, 2) the volume variation
is at least partly effected with a compressor attached to the
etching bath, and 3) the pressure variation is at least partly
effected by at least one of removal of a gas and a liquid from the
etching bath or by addition of at least one of the gas and the
liquid thereto, the removal is effected with a first vacuum pump
connected to the etching bath and the addition is effected with a
gas inlet connected to the etching bath.
[0004] We also provide a method of detaching a growth substrate
from a layer sequence including A) providing at least one wafer
composite including the growth substrate, the layer sequence
applied to the growth substrate, and a carrier attached to a top
surface of the layer sequence remote from the growth substrate,
wherein the layer sequence is patterned in a multiplicity of
regions spaced apart in lateral directions and separated from one
another by a multiplicity of separating trenches, and the
separating trenches connect to one another, B) introducing the at
least one wafer composite into an etching bath containing an
etching solution such that the etching solution is located at least
in regions within the separating trenches, C) repeatedly varying
the pressure of a base pressure prevailing in the etching bath
using at least one pressure variation device, and D) detaching the
growth substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIGS. 1A and 1B show examples of a wafer composite described
herein for performing a method described herein.
[0006] FIGS. 2 to 4, 5A, 5B and 6 show examples of a vacuum system
for performing a method described herein.
LIST OF REFERENCE NUMERALS
[0007] 1 wafer composite [0008] 1d outer edge [0009] 10 growth
substrate [0010] 11 layer sequence [0011] 11a top surface [0012]
111 sacrificial layer [0013] 112 semiconductor layer stack [0014]
13 carrier [0015] 14 separating trenches [0016] 15 regions [0017]
2, 2' enlarged view [0018] 20 gas bubbles [0019] 21 direction of
movement [0020] 22 convection [0021] 3 vacuum system [0022] 30
pressure change controller [0023] 301 control connections [0024] 31
first vacuum pump [0025] 32 pump unit [0026] 33 second vacuum pump
[0027] 34 vacuum reservoir [0028] 351 compressor [0029] 352 gas
inlet [0030] 36 chemical reservoir [0031] 37 Woulf's flask [0032]
38 pressure gauge [0033] 39 valve [0034] 310 vacuum connection
[0035] 311 chemical feed inlet [0036] 312 vacuum line [0037] 313
chemical outlet [0038] 314 overpressure line [0039] 315 DI water
feed inlet [0040] 317 water spray nozzle [0041] 321 discharge
outlet [0042] 322 outflow [0043] 323 inflow [0044] 40 etching bath
[0045] 40a top side of the etching bath [0046] 401 screw clip
[0047] 402 seal [0048] 403 screw seal [0049] 41 ultrasonic bath
[0050] 42 ultrasonic radiation [0051] 43 heater [0052] 44 etching
solution [0053] 45 gas [0054] 47 wafer holder [0055] 50 buffer
chamber [0056] 51 hydraulic plunger/piston [0057] 52 pivot joint
[0058] 53 pivot arm
DETAILED DESCRIPTION
[0059] We provide a method of detaching a growth substrate. The
method is especially suitable for separating a growth substrate
from a layer sequence applied to the growth substrate.
[0060] At least one wafer composite may be provided. The wafer
composite has a main extension plane in which it extends in lateral
directions. Perpendicularly to the main extension plane, in a
vertical direction, the wafer composite has a thickness that is
small compared to the maximum extent of the wafer composite in the
lateral directions.
[0061] The wafer composite comprises a growth substrate and a layer
sequence applied to, especially grown at least partly epitaxially
on, the growth substrate. The layer sequence can comprise a
semiconductor layer stack having a multiplicity of semiconductor
layers. In particular, the layer sequence can have at least one
active layer for absorption and/or emission of light, or an
integrated circuit. For example, the layer sequence is intended for
use in a light-emitting diode chip, a photodiode chip and/or a
solar cell chip. The layer sequence can further comprise a
sacrificial layer, by which the semiconductor layer stack can be
joined to the growth substrate.
[0062] The sacrificial layer can be selectively etchable to the
semiconductor layer stack and/or the growth substrate. In other
words, there is at least one etching solution having a
substantially higher etching rate in respect of the material of the
sacrificial layer than in respect of the material of the
semiconductor layer stack and/or the growth substrate. The
sacrificial layer can have a high aluminum content. In particular,
the sacrificial layer can be formed, for example, with
Al.sub.nGa.sub.1-nAs, where 0.6.ltoreq.n.ltoreq.1, preferably
0.7.ltoreq.n.ltoreq.1.
[0063] The wafer composite further comprises a carrier attached to
a top surface of the layer sequence remote from the growth
substrate. For example, the carrier is mechanically joined to the
layer sequence by a solder layer that can directly adjoin the top
surface and the carrier. The carrier can be formed, for example,
with a ceramic material, a plastics material, a metal and/or a
semiconductor material. The carrier can be, for example, an
electrical connection carrier.
[0064] The layer sequence may be patterned in a multiplicity of
regions spaced apart in lateral directions and separated from one
another by a multiplicity of separating trenches. The separating
trenches can be recesses in the layer sequence. The separating
trenches have a width given by the minimum extent of the separating
trenches in at least one lateral direction. For example, the width
is at least 1 .mu.m and at most 1000 .mu.m, preferably at least 2
.mu.m and at most 200 .mu.m and especially preferably at least 5
.mu.m and at most 100 .mu.m. Along the vertical direction the
separating trenches have a height corresponding, for example, to
the maximum extent of the layer sequence in the vertical direction.
The height and/or the width of the separating trenches can in
particular be the feature sizes thereof.
[0065] The separating trenches laterally connect to one another. In
other words, the separating trenches are intercommunicating. In
particular, the separating trenches connect to one another such
that, from a center of the wafer composite along the separating
trenches to an outer edge of the wafer composite, the separating
trenches have a minimum cross-section of at least 1 .mu.m.sup.2,
preferably at least 1000 mm.sup.2, preferably at least 4
.mu.m.sup.2 and at most 40 mm.sup.2 and especially preferably at
least 10 .mu.m.sup.2 and at most 1 mm.sup.2. The cross-section is
in particular given by the feature sizes of the separating
trenches.
[0066] For example, the separating trenches surround the regions of
the layer sequence in a frame-like manner. In particular, the
regions of the layer sequence created by the separating trenches
correspond to the chips to be produced, for example, the
light-emitting diode chips, photodiode chips and/or solar cell
chips to be produced.
[0067] The at least one wafer composite may be introduced into an
etching bath containing an etching solution. The etching bath can
especially be a reaction chamber at least partly filled with the
etching solution. The etching bath can additionally contain a gas
such as, for example, air. In particular, some or all of the gas
can be in the form of gas bubbles located within the etching
solution. A total volume of the etching bath can then be given by
the sum of a liquid volume of the etching solution and a gas volume
of the gas. In a borderline case, the etching bath can be
completely full of the etching solution at the beginning of the
process, the total volume at the beginning of the process then
being given by the liquid volume. In that borderline case, it is
still possible for gas bubbles to be formed within the etching
solution during the etching process, with the result that a gas
volume is generated.
[0068] The etching solution can be acid such as, for example, 10%
hydrofluoric acid. In particular, the etching solution can be
suitable for selective etching of the sacrificial layer of the
layer sequence. A direct contact between the etching solution and
the sacrificial layer can accordingly result in a chemical reaction
in which the sacrificial layer reacts with the etching solution. In
particular, the sacrificial layer is thereby dissolved or detached
from the layer sequence and/or the growth substrate. Furthermore,
reaction gases and/or reaction products can be formed. A "selective
etching" of the sacrificial layer takes place, for example, when
the etching solution has an etching rate in respect of the material
of the sacrificial layer that is at least a factor 10, preferably a
factor 100 and especially preferably a factor 1000, above the
etching rate in respect of the material of the layer sequence, of
the growth substrate and/or of the carrier.
[0069] Introduction of the wafer composite into the etching bath is
effected such that the wafer composite is covered at least in
regions by the etching solution. Furthermore, the etching solution
is located at least in regions within the separating trenches. In
particular, the etching solution can in regions be in direct
contact with the layer sequence, especially the sacrificial layer.
For example, the etching solution is introduced into the separating
trenches by exploiting the capillary effect. In that case, it is
possible for the etching solution to be sucked into the separating
trenches as into a thin tube.
[0070] For example, the at least one wafer composite can first be
introduced into the etching bath which has not yet been filled with
the etching solution. The etching solution at a suitable
temperature is then introduced or sucked into the etching bath.
[0071] The pressure of a base pressure prevailing in the etching
bath may be repeatedly varied. The base pressure can especially be
the average pressure prevailing in the etching bath. For example,
the base pressure is at least 0.01 bar and at most 70 bar,
preferably at least 0.1 bar and at most 30 bar and especially
preferably at least 0.5 bar and at most 5 bar.
[0072] The pressure variation is effected using at least one
pressure variation device. The pressure variation device can in
particular be a pump apparatus such as, for example, a vacuum pump,
and/or a volume variation device such as, for example, a
compressor, a gas inlet and/or a volume reservoir such as, for
example, a vacuum reservoir. In particular, the pressure variation
device can comprise a plurality of components with which the
pressure within the etching bath can be varied.
[0073] In the method of detaching a growth substrate from a layer
sequence, the method may comprise the following steps: [0074] A)
providing at least one wafer composite comprising the growth
substrate, the layer sequence applied to the growth substrate, and
a carrier attached to a top surface of the layer sequence remote
from the growth substrate, wherein [0075] the layer sequence is
patterned in a multiplicity of regions spaced apart in lateral
directions and separated from one another by a multiplicity of
separating trenches, and [0076] the separating trenches laterally
connect to one another, [0077] B) introducing the at least one
wafer composite into an etching bath containing an etching solution
such that the etching solution is located at least in regions
within the separating trenches, [0078] C) repeatedly varying the
pressure of a base pressure prevailing in the etching bath using at
least one pressure variation device, and [0079] D) detaching the
growth substrate.
[0080] The method steps can especially be carried out in the order
indicated.
[0081] At least the etching solution located within the separating
trenches may have the gas bubbles. The gas bubbles can be small
bubbles formed as a result of the reaction of the sacrificial layer
with the etching solution. In other words, the gas bubbles can be
reaction products of the etching process. By the pressure variation
within the etching bath the volume of the gas bubbles in the
separating trenches is deliberately altered. In particular, at low
pressure the gas bubbles are large and at high pressure small
compared to the feature sizes of the separating trenches. The
pressure variation accordingly generates a constant pulsing of
expansion and compression of the gas bubbles in the solution. That
alteration in the volume of the gas bubbles then forces a
convection of the etching solution within the separating
trenches.
[0082] Our method especially pursues the idea of increasing the
throughflow speed of the etching solution through the separating
trenches by varying the pressure within the etching bath. Since the
etching solution can be a non-compressible liquid, it is possible
in particular to vary the pressure of the gas or the gas bubbles in
the etching bath. Without the use of the pressure variation during
the detachment of a growth substrate from a layer sequence, the
mass transport of the reaction products or reactants in the
separating trenches is insufficient. Accordingly, the convection in
the separating trenches must be forced, it being necessary also to
overcome the interfacial energies as a result of the gas bubbles.
The increased throughflow speed enables the detachment speed to be
increased. Using the method described herein it is accordingly
possible to accelerate wet-chemical processes which are
transport-limited by small feature sizes and possible generation of
gas.
[0083] In particular, as a result of the pressure variation the
volume of the gas bubbles located in the etching solution within
the separating trenches can be altered and accordingly the
throughflow through the separating trenches can be increased. Even
gas bubbles which in the case of small feature sizes are confined
by capillary forces are mobilized by the pressure variation so that
the transport of the etching solution is then no longer impeded,
but is controlled by such forced convection. Furthermore, in the
course of the pressure variation the gas bubbles confined in the
separating trenches rise as a result of the superposed hydrostatic
pressure and can thus leave the separating trenches.
[0084] The pressure variation may comprise a change between a
maximum pressure and a minimum pressure. In particular, a temporal
change between the maximum pressure and the minimum pressure takes
place. Preferably, a repeated temporally periodic change between
the minimum pressure and the maximum pressure takes place. The
minimum pressure can be the saturated vapor pressure of the etching
solution.
[0085] The maximum pressure may correspond to at least 1.5 times,
preferably at least 2 times and especially preferably at least 10
times, the base pressure. Furthermore, the minimum pressure
corresponds to at most 0.5 times, preferably at most 0.2 times and
especially preferably at most 0.1 times, the base pressure. For
example, the base pressure is 1 bar. For example, the minimum
pressure and the maximum pressure can then be 0.2 bar and 2 bar,
respectively.
[0086] The pressure variation may take place temporally
periodically at a variation frequency of at least 0.01 Hz,
preferably at least 0.1 Hz and especially preferably at least 0.5
Hz, and at most 15 kHz, preferably at most 10 kHz and especially
preferably at most 500 Hz. For example, a change between the
maximum pressure and the minimum pressure can take place at the
variation frequency. In particular, the variation frequency is
matched to the low flow speed of the etching solution within the
separating trenches. Alternatively or in addition, the variation
frequency can be matched to the mobility of the etching solution in
the separating trenches.
[0087] The pressure variation may include a volume variation
between a minimum volume and a maximum volume around a base volume
of the etching bath. In other words, the volume of the etching
bath, especially the gas volume of the etching bath, is increased
and reduced, preferably temporally periodically to thus generate a
pressure variation within the etching bath. The base volume can be
the gas volume of the etching bath before the volume variation was
begun. The volume variation can in particular be carried out using
the volume variation device.
[0088] The maximum volume may correspond to at least 5 times,
preferably at least 10 times and especially preferably at least 40
times, the base volume and/or the minimum volume corresponds to at
most 0.8 times, preferably at most 0.5 times and especially
preferably at most 0.3 times, the base volume.
[0089] Prior to step B) a buffer chamber may be provided and
attached to the etching bath and provided connected thereto. For
example, the buffer chamber is a vacuum chamber and/or an
overpressure chamber. The buffer chamber can connect to the etching
bath directly or by vacuum lines. The buffer chamber can especially
be cylindrical and have a swept volume. The minimum volume then
corresponds to the net volume of the etching bath and the
connecting vacuum line, while the maximum volume corresponds to the
volume of the etching bath inclusive of the available swept volume.
The volume variation that can be generated, that is to say the
difference between the minimum volume and the maximum volume that
can be generated, increases with the ratio of the swept volume to
the volume of the etching bath and the vacuum lines. In particular,
a ratio of the maximum volume to the minimum volume can be, for
example, 10:1.
[0090] The volume variation may be effected by a movement of a
piston introduced into the buffer chamber or of a hydraulic plunger
introduced into the buffer chamber. In particular, the swept volume
can be added to or removed from the volume of the etching bath by
the piston or the hydraulic plunger. Accordingly, by a periodic
movement of the piston or hydraulic plunger, for example, using a
crankshaft, a change in pressure is generated at a crankshaft
frequency which can be the variation frequency. In particular, the
crankshaft frequency can be at least 0.01 Hz, preferably at least
0.1 Hz and especially preferably at least 1 Hz, and at most 15 kHz,
preferably at most 10 kHz and especially preferably at most 500 Hz.
For example, the crankshaft frequency can lie at least in the
infrasonic range.
[0091] The buffer chamber may have at least one variation valve.
The volume variation is effected by closing and/or opening the
variation valve. The variation valve can be provided in addition to
or as an alternative to the piston or hydraulic plunger. The
variation valve can be actuated individually, for example, with a
piezo. As a result, it is possible to adjust as desired an
additional overpressure or underpressure, or the minimum pressure
or maximum pressure, in the etching bath. By the use of the
variation valve it is possible to achieve high variation
frequencies and high volume variations.
[0092] The volume variation may be at least partly effected with a
compressor attached to the etching bath. Using the compressor, the
volume can be reduced, for example, to a minimum volume in a
simplified manner.
[0093] The pressure variation may be at least partly effected by
removal of gas and/or liquid from the etching bath or by addition
of gas and/or liquid thereto. The pressure variation is then
generated by a variation of the amount of gas or amount of liquid
in the etching bath.
[0094] The removal of gas and/or liquid may be effected with a
first vacuum pump connected to the etching bath. Furthermore, the
addition of gas and/or liquid may be effected with a gas inlet or
liquid inlet connected to the etching bath. In particular, by the
gas inlet it is possible to introduce nitrogen gas into the
system.
[0095] The first vacuum pump can additionally have a ventilation
valve through which reaction gas formed during the etching process
can be discharged. As a result, a pressure variation can
effectively be generated within the etching bath. A further
advantage of using the first vacuum pump is that the minimum
pressure within the etching bath achievable with a vacuum pump is
lower than the saturated vapor pressure of the etching solution. As
a result, the minimum pressure achievable is limited so that the
etching solution can be brought to a boil without increasing the
process temperature. This enables additional gas bubbles to be
generated within the separating trenches. In a detachment without
intrinsic development of gas bubbles, it is in this way possible to
generate gas bubbles to increase convection.
[0096] Especially strong and rapid pressure variations can be
generated if, in addition to the reaction products, little or no
additional gas volume is present in the etching bath. This can be
achieved, for example, by additionally pumping away the reaction
products with a second vacuum pump and/or the first vacuum pump.
Furthermore, in a small gas volume the pressure difference can be
precisely adjusted and controlled with a piston processor or with a
hydraulic plunger.
[0097] Between the etching bath and the first vacuum pump there can
additionally be connected the volume reservoir which can have a
large volume relative to the volume of the etching bath. As a
result, the pressure drop in the etching bath can be additionally
accelerated. Alternatively or in addition, compressed gas can be
introduced into the etching bath by way of a ventilation side of
the first vacuum pump to accelerate an increase in pressure, the
etching bath in this case being of overpressure-resistant
construction.
[0098] Prior to or during step C) the etching bath may be
introduced into an ultrasonic bath. An ultrasonic radiation is then
applied to the etching bath by the ultrasonic bath. The ultrasonic
radiation enables the surface tension to be reduced, with the
result that the adhesion of the gas bubbles to the walls of the
separating trenches is reduced. As a result of the high frequencies
of the ultrasonic radiation in the region of a few kHz, small
amplitudes of the radiation can be used. It has been shown that a
normally to be expected physical destruction of the surfaces of the
layer sequence, of the carrier and/or of the growth substrate does
not occur, but rather the movement of the etching solution in the
separating trenches can be increased by ultrasonic radiation.
[0099] The etching bath may be heated to a process temperature
using a heater. The process temperature may be at least 0 C,
preferably at least 20 C and especially preferably at least 40 C,
and at most the temperature at the thermodynamic critical point of
the etching solution. An increase in the process temperature in
particular allows an increase in the base pressure. Accordingly, a
higher pressure variation can be generated in a simple manner
because a higher base pressure allows a higher amplitude. In
addition, as a result of the increased process temperature the
chemical reaction of the etching solution with the sacrificial
layer can be accelerated.
[0100] During steps B) to D) a wedge may be inserted between the
growth substrate and the carrier. In particular, the wedge is
inserted between the growth substrate and the layer sequence. A
wedge is especially a body in which two side faces converge at an
acute angle. Such a wedge serves especially as a feeler for the
progress of the detachment process because the penetration depth of
the wedge between the carrier and the growth substrate is increased
as the etching process progresses. Furthermore, the wedge can be
actively utilized to accelerate the detachment process by bending
up the wafer composite. An additional stress between the growth
substrate and the carrier, for example, as a result of a slight
curvature of the growth substrate and/or the carrier, can further
accelerate a detachment process.
[0101] It is also possible, using galvanic or electrochemical
etching, to accelerate the chemical reaction between the etching
solution and the sacrificial layer or to increase the selectivity
of the etching process to the growth substrate and/or the
carrier.
[0102] The method described herein is explained in greater detail
below with reference to examples and associated Figures.
[0103] In the Figures, elements that are identical or similar or
have identical action are denoted by the same reference numerals.
The Figures and the relative sizes of the elements illustrated in
the Figures to one another should not be regarded as to scale.
Rather, the size of individual elements may have been exaggerated
in the drawings for the purpose of better clarity and/or better
understanding.
[0104] An example of a wafer composite 1 described herein for
performing a method described herein is explained in greater detail
with reference to the diagrammatic sectional view of FIG. 1A. The
wafer composite 1 comprises a growth substrate 10, to which a layer
sequence 11 having a sacrificial layer 111 and a semiconductor
layer stack 112 has been applied. The layer sequence 11 has a top
surface 11a remote from the growth substrate 10. A carrier 13 has
been applied to the top surface 11a. The carrier 13 can be, for
example, a connection board and/or a circuit board. It is possible
for the carrier 13 to comprise as material silicon, germanium,
sapphire and/or some other, preferably crystalline, material which
is not etched by the etching solution. Furthermore, the growth
substrate 10 can comprise silicon, germanium, sapphire and/or the
other material not etched by the etching solution or can consist of
one of those materials.
[0105] The layer sequence 11 is patterned in a multiplicity of
laterally spaced-apart regions 15. The regions are separated from
one another by separating trenches 14. The separating trenches 14
pass completely through the layer sequence 11 in the vertical
direction.
[0106] A further example of a wafer composite 1 described herein is
explained in greater detail with reference to the diagrammatic plan
view of FIG. 1B. The wafer composite 1 has a multiplicity of
regions 15 separated from one another by the separating trenches
14. The separating trenches 14 encompass the regions 15 in a
frame-like manner. In particular, the separating trenches 14
intercommunicate with/and connect to an outer edge 1d of the wafer
composite 1.
[0107] An example of a vacuum system 3 for a method described
herein is explained in greater detail with reference to the
diagrammatic view of FIG. 2. The pressure variation device 3
comprises an etching bath 40. The etching bath 40 has in this case
purely by way of example been introduced into an ultrasonic bath 41
with which an ultrasonic radiation 42 can be applied to the etching
bath 40. Furthermore, the etching bath 40 can be heated to a
process temperature with a heater 43.
[0108] The vacuum system 3 comprises a multiplicity of pressure
gauges 38 and valves 39. The valves 39 can be shut-off valves,
especially chemical-resistant shut-off valves. Furthermore, the
vacuum system 3 comprises a multiplicity of vacuum connections 310,
the function of which is explained in greater detail
hereinbelow.
[0109] A chemical reservoir 36 connects to the etching bath 40 by
way of a chemical feed inlet 311. By the chemical reservoir 36, in
particular the etching solution 44 can be introduced into the
etching bath 40.
[0110] A compressor 351 and/or a gas inlet 352 connects to the
etching bath 40 by way of the overpressure line 314. By the
overpressure line 314, an overpressure can be generated in the
etching bath 40. For example, generation of the overpressure is
effected by reducing the volume, especially a gas volume 45 (not
shown in FIG. 2), within the etching bath 40 using the compressor
351. Alternatively or in addition, the pressure in the etching bath
40 can be increased with a gas inlet 352.
[0111] Furthermore, the etching bath 40 can connect by way of a
vacuum line 312 to a vacuum reservoir 34 and/or to a first vacuum
pump 31. The first vacuum pump 31 can be, for example, a
chemical-resistant vacuum pump such as a scroll pump, a diaphragm
pump or a water-jet pump. The first vacuum pump 31 can also have a
cold trap preferably having a temperature below the freezing point
of the etching solution. For example, the cold trap contains liquid
nitrogen or dry ice. In addition, a discharge outlet 321 is
attached to the first vacuum pump 31. By the discharge outlet 321,
for example, reaction gases formed during the reaction of the
etching solution 44 with the sacrificial layer 111 can be removed
from the system.
[0112] The vacuum reservoir 34 can be, for example, an evacuated
vessel that can connect by way of the valves 39 to the etching bath
40 to thus accelerate a pressure drop in the etching bath 40. In
particular, there can be a vacuum in the vacuum reservoir 34, for
example, with a pressure of at most 0.5 bar, preferably at most
0.05 bar.
[0113] The first vacuum pump 31, the vacuum reservoir 34, the
compressor 351 and the gas inlet 352 connect to a pressure change
controller 30 by way of control connections 301. The pressure
change controller 30 is in particular programmable and serves for
the deliberate adjustment of the pressure in the etching bath
40.
[0114] The vacuum system 3 also has a chemical outlet 313. A DI
water feed inlet 315 connects to the chemical outlet 313. The DI
water feed inlet 315 leads to a pump unit 32 that can be, for
example, a water feed inlet or a water-jet pump. The pump unit 32
has an outflow 322 and an inflow 323. The DI water feed inlet 315
serves in particular for flushing the wafer composite 1 within the
etching bath 40.
[0115] Furthermore, the etching bath 40 connects to a second vacuum
pump 33 by way of the chemical outlet 313. The second vacuum pump
33 can likewise be a chemical-resistant vacuum pump such as, for
example, a scroll pump, a diaphragm pump or a water-jet pump. The
second vacuum pump 33 connects to the chemical outlet 313 by way of
a Woulf's flask 37 having a pressure gauge 38. By way of the
chemical outlet 313 the etching solution 44 can be removed from the
etching bath 40. For that purpose, the second vacuum pump 33
likewise has an outflow 322.
[0116] The vacuum system 3 can additionally have a gas detector
with which the reaction gases formed can be detected. As a result,
the end of the process can be determined accordingly. For example,
the reaction gases can be collected at a top side 40a of the
etching bath 40. In particular, the top side 40a can have a
funnel-like shape with a measuring cylinder having a readable scale
being attached at the highest point. When the liquid level sinks,
the amount of gas can be read off at the bottom of the meniscus of
the scale.
[0117] A further example of a vacuum system 3 for a method
described herein of detaching a growth substrate 10 is explained in
greater detail with reference to the diagrammatic view of FIG. 3.
FIG. 3 shows a cross-section through the etching bath 40. At least
one wafer composite 1 has been introduced into the etching bath 40.
Furthermore, the etching bath 40 contains the etching solution 44
and a gas 45, which can be, for example, air. A liquid volume of
the etching solution 44 and a gas volume of the gas 45 then
together form a total volume of the etching bath 40. It is also
possible, however, for the etching bath 40 to be completely full of
the etching solution 44. The etching solution 44 can make up at
least 80%, preferably at least 90% and especially preferably at
least 95%, of the wafer composite 1.
[0118] At a top side 40a of the etching bath 40 there are two
vacuum ports, with respective vacuum connections 310 being
connected to the etching bath 40 by way of screw seals 403. In
particular, the top side 40a of the etching bath 40 can have a
lid.
[0119] On the left-hand side of the top side 40a of the etching
bath 40 there is attached the vacuum line 312 that connects to the
etching bath 40 by way of a valve 39. The first vacuum pump 31 (not
shown in FIG. 3) is attached to the vacuum line 312. By way of the
vacuum line 312, the pressure within the etching bath 40 can be
reduced with the first vacuum pump 31.
[0120] On the right-hand side of the top side 40a of the etching
bath 40 there is attached the overpressure line 314 that connects
to the compressor 351 and/or to the gas inlet 352 (not shown in
FIG. 3). By the compressor 351 or the gas inlet 352, the pressure
within the etching bath 40 can be increased by way of the
overpressure line 314.
[0121] Furthermore, FIG. 3 diagrammatically shows the effect of the
pressure variation by the vacuum line 312 and the overpressure line
314. In particular, a preferred direction of movement 21 of the
etching solution 44 in the wafer composite 1 is generated.
[0122] The two enlarged views 2, 2' of FIG. 3 in each case show a
portion of the wafer composite 1 introduced into the etching bath
40. The wafer composite 1 contains the separating trenches 14,
within which the etching solution 44 has been introduced. In
addition, the separating trenches 14 have gas bubbles 20. For
example, the gas bubbles 20 can have been generated by the chemical
reaction of the etching solution 44 with the sacrificial layer 111
(not shown) of the layer sequence 11. The left-hand enlarged view 2
shows the gas bubbles 20 at a high pressure, especially the maximum
pressure. The volume of the gas bubbles 20 is small at a high
pressure. The right-hand enlarged view 2' shows the gas bubbles 20
at a lower pressure, especially the minimum pressure. As a result
of the reduction in pressure, the volume of the gas bubbles 20 is
increased and a convection 22 occurs. As a result of such
convection 22, a movement of the gas bubbles 20 within the
separating trenches is generated.
[0123] A further example of a vacuum system 3 used for a method
described herein is explained in greater detail with reference to
the diagrammatic views of FIG. 4. The example shown corresponds to
that of FIG. 3, but further technical components are present as
follows. A plurality of wafer composites 1, so-called racks, have
been introduced into the etching bath 40 within the etching
solution 44 by a wafer holder 47. Screw clips 401 and seals 402 are
used to close the etching bath 40. Furthermore, within the etching
bath 40 there is provided a water spray nozzle 317. The water spray
nozzle 317 can connect, for example, to the DI water feed inlet 315
(not shown in FIG. 4). By the water spray nozzle 317, it is
possible, for example, to clean and/or flush the wafer composite 1
after the method has been carried out so that any etching solution
44 possibly present on the wafer composite 1 is removed
therefrom.
[0124] A further example of a vacuum system 3 for a method
described herein is explained in greater detail with reference to
the diagrammatic view of FIG. 5A. Unlike the vacuum system 3 of
FIG. 4, the vacuum system 3 of FIG. 5A additionally comprises a
buffer chamber 50 laterally attached to the etching bath 40. In the
example of FIG. 5A, the volume of the buffer chamber 50 is coupled
directly to the etching solution 44, that is to say to the liquid
volume. The buffer chamber 50 is in this case a cylindrical chamber
having in its interior a hydraulic plunger 51 or a piston 51. By a
pivot joint 52 and a pivot arm 53, the piston 51 or the hydraulic
plunger 51 can be moved such that a swept volume of the buffer
chamber 50 can be added to the volume of the etching bath 40 or
removed therefrom. As a result, it is possible to vary the volume
within the etching bath 40 and accordingly generate a pressure
variation within the etching bath 40. The buffer chamber 50 can
have additional variation valves (not shown in FIG. 5A) that can be
controlled individually to thus generate, as desired, overpressure
or underpressure in the etching bath 40.
[0125] A further example of a vacuum system 3 for a method
described herein is explained in greater detail with reference to
the diagrammatic view of FIG. 5B. Unlike the vacuum system 3 of
FIG. 5A, the buffer chamber 50 is attached to the top side 40a of
the etching bath 40 and accordingly is in contact with the gas 45.
In the example shown, the buffer chamber 50 is therefore coupled to
the gas volume of the gas 45.
[0126] It is also possible (not shown in the Figures) for the
buffer chamber 50 to be attached to the etching bath 40 such that
the volume of the buffer chamber 50 simultaneously contacts the gas
45 and the etching solution 44.
[0127] A further example of a vacuum system 3 of performing a
method described herein is explained in greater detail with
reference to the diagrammatic plan view of FIG. 6. A plan view onto
the etching bath 40 is shown. This Figure shows the ports for the
water spray nozzle 317, and also the ports for the chemical feed
inlet 311, the vacuum line 312, the chemical outlet 313, the
overpressure line 314 and the DI water feed inlet 315.
[0128] Unlike an alternative method in which movement of the
etching solution is increased by an externally applied pressure
gradient and not by a pressure variation, in this method the wafer
composite 1 is not sealed. Accordingly, instead of providing each
wafer composite with vacuum seals, in this case processing can
simply be carried out on the rack scale and is accordingly suitable
for mass production.
[0129] This application claims priority of DE 10 2015 104 147.2,
the subject matter of which is incorporated herein by
reference.
[0130] The description of our methods with reference to the
examples does not limit this disclosure thereto. Rather, this
disclosure encompasses any novel feature and any combination of
features, including in particular any combination of features in
the appended claims, even if the feature or combination is not
itself explicitly defined in the claims or examples.
* * * * *